Linear actuators with piston means displaced by fluid or air pressure are typically used to control the opening and closing of valves, e.g., gate valves, globe valves, sluice gates and cone valves.
Many situations exist where electrically operated control mechanisms, such as the valves just noted, and the like, if locked in an operative position by an interruption of electric power, can create awkward, difficult, and even hazardous conditions.
The present inventor has created a fail safe hydraulic actuator system, particularly one featuring a linear actuator, which upon loss of electric power instantly and automatically returns the control mechanism which is being monitored to the inoperative position (i.e., either open or closed). Moreover, the present invention provides a unique means for controlling the fail safe means whereby fluid can not be delivered to the linear actuator until a pressurized storage means has been charged with sufficient fluid so as to enable the storage means to return the linear actuator to its inoperative position in the event of a power loss.
The present inventor is not aware of any other fail safe electric linear actuator which automatically returns the control mechanism to its inoperative position during a power loss. U.S. Pat. No. 4,757,684 (Wright), which issued on Jul. 19, 1988, discloses the use of a reversible means for storing energy as a fail safe means on a rotary actuator. The reversible means for storing energy is attached to the fluid-driven vaned torque actuator by a shaft such that as the torque actuator is rotated by means of a fluid, the reversible means simultaneously stores energy. When the electric power supply is interrupted, a valve means is de-energized and opened, permitting energy stored in the reversible means to return the shaft, thereby restoring the fail safe actuator device and the control mechanism to their initial inoperative position. The reversible means for storing energy mechanically is a torsion spring. For space conservation, a flat clock type spring could be substituted for the torsion spring. It is also suggested that an accumulator having reverse power be used in place of the torsion spring. However, this patent does not describe how the flat clock type spring or accumulator would function as a fail safe device.
The present invention also provides many additional advantages which shall become apparent as described below.